1. Field of the Invention
The present invention relates to valve stem seal assemblies for use in internal combustion engines, and more particularly to the design and construction of molded elastomeric seal components employed in such seal assemblies.
2. Description of the Related Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves, supported for reciprocal motion within valve guides, include integral elongated stems extending away from the engine cylinder heads, the ends of the stems typically interacting with rotating overhead cams for cyclic or repeated opening and closure of the valves against the force of valve return springs during the combustion cycle. In order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must obviously exist between the valve guide and the moving stem. In fact, a plurality of such valve stems move reciprocally in valve guides, to and from the cylinder head, each within its individual guide. So-called valve stem seal assemblies are used to seal against leakage of oil through a mechanical clearance path between each annular engine valve guide and its associated valve stem.
As is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotatable with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of similar construction and both include stems integrally affixed to the valves.
In some engines, a unitary elastomeric valve stem seal component is fitted over or atop each valve guide, wherein the seal component is frictionally mounted directly to the guide. In other cases the seal is encased within or otherwise secured to a rigid, typically metal, seal retainer to form an assembly, as required in some applications to assure proper securement of the seal to the guide. Those skilled in the art will appreciate that pluralities of such elastomeric valve stem seal components are employed in typical engines. In the case of a V-8 engine, a total of at least 16 valve stem seals are employed, one for each intake and one for each exhaust at each cylinder, depending on actual number of valves employed per cylinder in a particular engine.
Traditional elastomeric seal components have been fabricated using techniques that address only the chemical compositions of various elastomeric materials employed. Thus, even in environments wherein tougher elastomeric materials may be required, only the material compositions have been modified to enhance strength of materials as desired. In many cases, this approach has been fraught with significant technical complexity, and has yielded minimal results.
In addition, traditional manufacture of such seals has been only on a unitary batch basis, or via one batch at a time. Thus, although much progress has been achieved in the art of valve stem seal design and construction, cost-effective techniques for enhancement of strength of materials, along with streamlined manufacturing techniques remain areas in need of additional improvement.
The improved valve stem seal component of the present invention overcomes the traditional compositional limitations of prior art elastomeric seals with respect to enhancement of strength of materials, and also significantly streamlines valve stem seal component manufacturing, both in a cost-effective assembly line process.
The present invention provides an elastomeric seal component adapted for installation directly atop of a valve guide of an internal combustion engine. A plurality of such seal components is contemplated for use in an engine, each component designed for insertion over each engine valve guide of a given engine. Each component is adapted for continuously and sealingly engaging an associated reciprocally movable valve stem. The seal component body incorporates an interior circumferential aperture containing at least one radially inwardly directed, resilient, sealing lip adapted to engage the stem to minimize escape of oil lubricant from the engine along a path between the valve guide and the reciprocally movable valve stem.
The unique seal component incorporates fabric reinforcement within the annular jacket body of the seal body. In one preferred form, the fabric is positioned intermediately between two layers of the seal body; i.e. between an inner layer and an outer layer.
Finally, two manufacturing methods are presented for manufacture of the seal component. A first provides for extrusion of a tube having the fabric reinforcement layer already provided between inner and outer layers. A cutting die incorporates a push ring adapted to move the component along a staged molding assembly process. A series of threaded core pins are utilized for conveyance of the component in the fabrication process from one stage to the next. The preferred method consists of extruding a rubber tube and cover over a series of threaded core pins, the tube including a fabric reinforcement material positioned intermediate the tube layers; cutting a portion of the rubber tube to a predetermined length; molding the predetermined length of the tube to produce an annular valve stem seal component; curing the molded component; and removing the component from the mold.
An alternate method, called a transfer mold approach, provides molding an inner tube over a threaded core pin; applying a spiral knit reinforcement fabric to the exterior of the inner tube; molding a cover to the tube so as to directly overlie the reinforcement fabric to thus form a fabric reinforced valve stem seal; curing the seal component; and then removing the seal component from the core pin.